Electrostatic printing and developing

ABSTRACT

IN THE PARTICULAR EMBODIMENTS OF THE INVENTION DESCRIBED HEREIN, ELECTROSTATIC CHARGE IMAGES ARE FORMED ON THE ADJACENT ENGAGING SURFACE OF A POTOCONDUCITVE INSULATING LAYER AND ANOTHER INSULATING LAYER BY OPTICAL EXPOSURE THROUGH THE PHOTOCONDUCTIVE INSULATING LAYER. IN ONE EMBODIMENT THE LAYERS ARE DISPOSED ON THE OUTSIDE SURFACES OF FIRST AND SECOND ROTATING DRUMS, RESPECTIVELY, AND A LIGHT SOURCE WITHIN ONE DRUM PROJECTS THE IMAGE OF AN ORIGINAL DISPOSED ON THE INNER SURFCE OF THE DRUM TO THE PHOTOCONDUCTIVE INSULATING LAYER DISPOSED ON THE OUTER SURFACE THEREOF. ELECTROSTTIC CHARGE IMAGES ARE PRODUCED ON THE DRUM SURFACES AS A RESULT OF A POTENTIAL DIFFERENCE APPLIED ACROSS THEM AND THE CHARGE IMAGES ARE MOVED BY DRUM ROTATION TO A DEVELOPMENT ZONE WHEREIN THE IMAGES ARE RENDERED VISIBLE BY LIQUID OR POWDERED DEVELOPER. IN ANOTHER EMBODIMENT THE ELECTROSTATIC CHARGE IMAGE IS TRANSFERRED FROM THE INSULATING DRUM TO A FURTHER INSULATING DRUM UPON WHICH IT IS MOVED THROUGH A DEVELOPMENT ZONE.

June 27, 1972 E. F. MAYER 3,672,884

ELECTROSTATIC PRINTING AND DEVELOPING Original Filed Sept. 15, 1955 3 Sheets-Sheet 1 INVENTOR fold APO I, MA YER Zia, M,M,

ATTORN June 27, 1972 E. F. MAYER ELECTROSTATIC PRINTING AND DEVELOPING 3 Sheets-Sheet 2 Original Filed Sept. 15, 1953 l lllllll INVENTOR EDWARD 5 MA YER June 27, 1972 E. F. MAYER 3,672,884

ELECTROSTATIC PRINTING AND DEVELOPING Original Filed Sept. 15, 1953 3 Sheets-Sheet 3 INVENTOR.

EDWARD F. MAYER I A TTORNEYS United States Patent Office Patented June 27, 1972 US. Cl. 96-1 LY 13 Claims ABSTRACT OF THE DISCLOSURE In the particular embodiments of the invention described herein, electrostatic charge images are formed on the adjacent engaging surfaces of a photoconductive insulating layer and another insulating layer by optical exposure through the photocondiuctive insulating layer. In one embodiment the layers are disposed on the outside surfaces of first and second rotating drums, respectively, and a light source within one drum projects the image of an original disposed on the inner surface of the drum to the photooonductive insulating layer disposed on the outer surface thereof. Electrostatic charge images are produced on the drum surfaces as a result of a potential difference applied across them and the charge images are moved by drum rotation to a development zone wherein the images are rendered visible by liquid or powdered developer. In another embodiment the electrostatic charge image is transferred from the insulating drum to a further insulating drum upon which it is moved through a development zone.

This application is a continuation of application Ser. No. 571,644 filed Aug. 10, 1966, now abandoned, which was a continuation of application Ser. No. 380,285 filed Sept. 15, 1953, also now abandoned.

This invention relates to electrostatic printing and includes a novel electrostatic printing device as well as a novel method of utilizing such a device in the production of an ultimate visual reproduction of an elcctrostatically produced image.

There has been developed heretofore an electrophotographic device wherein a visible image is converted to an electrostatic image and the resulting electrostatic image is thereafter made visible by the deposition of carbon pow der in a pattern conforming to the electrostatic image. These prior art devices have required electrostatic charging of a photoconductive plate either by rubbing the plate with an electro-opposite material so as to produce a static charge on the plate or by means of a high voltage discharge tfrom a closely adjacent fine wire which, through the medium of the corona effect, sprays the surface of the photoconductive plate with charged ionized particles from the air.

As a modification of this concept, and useful only for the transmission of an electric signal corresponding to the electrostatic image and not adapted to the direct conversion of the electrostatic image into a visual image, there has been described in the patent to Carlson No. 2,277,013 a unitary electrophotographic element in which there may be established an electrostatic image corresponding to a visible light image. This electrophotographic element consists primarily of two layers of conductive material separated by two intervening layers of insulating material. One of the layers of insulating material is photoconductive and one of the conductive layers is transparent to light. When a light image is directed against the transparent conductive layer while maintaining a relatively low electric potential between the two conductive layers, there is established in one of the insulating layers an electrostatic image conforming in charge to the opacity of each incremental area of the light image. I have attempted to utilize this electrostatic element for the production therefrom of a visible image but have found that the subsequent charging of either of the conductive layers in the course of producing such a visible image destroys the electrostatic image.

As the result of an extensive investigation of the entire field of electrophotographic reproduction, I have discovered that if the single element of the aforementioned Carlson patent is divided into two separate elements, it is possible to obtain a visual image from the electrostatic image produced through the previous cooperation of these two elements. Thus, the electrophotographic device of my invention comprises a photoconductive element and an adjoining but separable electrostatic image-forming element. The photoconductive element advantageously comprises a transparent layer of electroconductive material and a contiguous layer of high resistance photoconductive material, and the electrostatic image-forming element comprises a layer of electrically insulating material and a contiguous layer of electrically conductive material. In some cases, the electroconductive material contiguous to the photoconductive material of the first-mentioned element may be opaque, in which case both components of the electrostatic image-formnig element are transparent. In either case, these two elements are so disposed with respect to one another that the layer of photoconductive material of one element adjoins the layer of insulating material of the other element. A source of electric po tential is provided which interconnects the transparent layer of electrically conductive material of one element with the electrically conductive material in the other element so as to provide the latter with a positive potential with respect to the former, and light means are also provided for directing a light image of the object toward and through the transparent layerof electrically conductive material in the direction of the contiguous layer of photoconductive material.

The method of producing a visual reproduction of a visual object with the electrophotographic device of my invention comprises directing a light image of the object through the transparent layer of electrically conductive material and thence through the contiguous high resistance photoconductive layer to the adjacent but separable layer of electrically insulating material backed by the supporting metal layer. A positive electric potential (or negative electric potential, if a negative image is desired) is applied to the supporting metal layer with respect to the transparent layer of electrically conductive material, thus establishing on the layer of insulating material an electrostatic reproduction of the light image. There is thereafter applied to the surface of the insulating material bearing the electrostatic reproduction of the image, after it has been separated from the previously adjoining photoconductive material, a dispersion of powdered carbon with the resulting formation on the surface of the separated insulating material of a carbon deposit comprising a visual reproduction of the aforesaid light image.

These and other novel features of the apparatus and method of my invention will be more fully understood from the following description taken in conjunction with the drawings in which each of FIGS. 1 through 6 represent a different modification of the two-element electrophotographic device of the invention.

The electrophotographic device shown in FIG. 1 is representative of the invention. In this device the two separate elements have the form of rotating drums 6 and 7. The drum 6 is of a transparent material 8 such as a glass cylinder. This cylinder is coated on its outer surface with a transparent conducting layer 9 such as a thin layer of tin oxide, or of evaporated gold with bismuth additions on the glass, or other conventional metallic conductors which are transparent in thin layers. The cylinder may also be formed of any transparent plastic with the transparent conductive coating upon its outer surfaces. A third alternative construction comprises a conductor chemically deposited upon the surface of a glass or plastic cylinder. The primary requisite of these materials is that they be of fairly low resistance, say 100 to 1000 ohms per square surface resistance, and that they be moderately transparent to visible light, say having a transparency of 50% to white light. These transparency requirements are arbitrary, and through the use of a higher or lower intensity light they may be greater or less, as the case may be. Over the aforementioned conductive coating 9 upon the cylinder there is formed a layer of a high resistance photoconductor 10. This photoconductive layer should have a resistivity in the dark of 10 ohm centimeters or greater, and a resistivity when exposed to the maximum light intensity of 10 ohm centimeters or less. Again, these resistivity values are arbitrary and may be varied as other factors are altered to meet various operating conditions. Selenium, arsenic selenide, zinc-cadmium sulfide, and many other substances, all of which have the aforementioned properties, are suitable. These photoconductive layers should be continuous and are advantageously deposited by vacuum deposition.

A second drum 7 is made of metal 11 coated with an insulating material 12. This insulating material may be any dielectric material such as polystyrene, methyl-methacrylate, cellulose acetate and other transparent cellulo'sic resins, or other plastic with low dielectric absorption. It may also comprise any of the conventional rubber-like materials of high dielectric strength and low dielectric absorption or an electrically insulating material such as zinc sulfide advantageously evaporated onto the metal drum in the form of a continuous layer. The layer of insulating material should be continuous and thick enough to withstand several hundred volts when such a field is applied across it. The insulating layer is also advantageously approximately the same thickness as the photoconductive layer placed upon the drum 6.

The two drums 6 and 7 are positioned so as to rotate in opposite directions in contact with each other along one element of each cylinder. In the center of the photoconductive drum 6 there is placed a fluorescent light 13 which possesses illumination characteristics similar to the sensitivity characteristics of the photoconductive material. A silver halide positive 14 to be reproduced is placed in contact with the interior of the drum 6 between the light source and the transparent conductive layer 9. This causes an image of the positive to be formed upon the photoconductive layer 10. In lieu of a directly positioned positive, any optical image focused upon the point of contact of the two drums 6 and 7 may be used. This optical image may be of the continuous tone type or simply a line negative.

As the two drums 6 and 7 rotate in opposite directions, their line of contact progresses around their surfaces. A potential source 15 of approximately 300 volts D0. is applied between the metal drum 11 and the conductive layer 9. This causes, at the line of contact between the surfaces of the two drums, the development of a charge upon the insulating layer 12 and the photoconductive layer 10 in the non-illuminated areas. The magnitude of this charge is inversely proportional to the illumination upon the chotoconductive layer at any particular point and is directly proportional to the potential applied. Each line of the picture at the line of contact between the drums is reproduced as the two drums rotate. Thus, there is built up upon both the insulating layer 12 and the photoconductive layer 10 a charge configuration inversely proportional to the illumination of each corresponding area of the negative.

It will be seen, accordingly, that the electrophotographic device described hereinbe'fore is composed of two adjoining but separable elements. One of these elements comprises the transparent conductive layer 9 and the photoconductive layer 10, and the other element comprises the insulating layer 12 and the conductive layer in contact therewith in the form of the metal drum 11. If it is desired to reverse the direction of the light impinging on the photoconductive layer, say by positioning the lightimage source within the electrostatic image-forming element, the drum 7 is replaced by a transparent layer of electrically conductive material contiguous to the insulating layer 12 and the layer 12 is composed of a transparent insulating material. In this case, the electrically conductive layer 9 may be opaque. It will also be clearly apparent that as the electrostatic image is formed on the insulating layer 12 in contact with the photoconductive layer 10 along the line of contact between these two elements, this image is immediately removed from the point of contact by the rotation of the drum 7. The electrostatic image thus removed from the photoconductive layer of the other element is readily amenable to subsequent development into the form of a visual image.

The development of a visual image from the aforementioned electrostatic image on the insulating layer 12 of the drum 7 may be effected by any of the conventional procedures described and used heretofore in this art. For example, a dry powder which is electrostatically charged and suspended in air :is attracted to charged areas comprising the electrostatic image on the insulating layer 12. A common material used as this powder is carbon black. Thus, by using a suspension of charged carbon black suspended in air and brought into contact with the electrostatic image-bearing portion of the insulating layer 12, there is produced on the insulating material a carbon deposition inversely proportional to the illumination of the original picture. This, therefore, is a positive image of the original picture or light image. The carbon black suspension is brought into contact with the surface of the insulating layer 12 in a zone 22 through which the electrostatic image passes soon after leaving its line of contact with the photoconductive layer 10 of the other element. The resulting. carbon black image is subsequently removed from the surface of the insulating layer 12 in a later zone 16 in the peripheral travel of this image during continued rotation of the drum 7. Removal of the carbon black image may be readily effected by bringing an adhesive-coated surface, or even an untreated surface, of a mov ng sheet of paper 17 into transient but relatively nonmoving contact with the moving surface of the insulating layer 12. The image is thus transferred to the paper, and the surface of the insulating layer 12 is subsequently reconditioned by its passage through a conventional cleaning zone 18 and a conventional electrical discharging zone 19 to prepare the surface of the insulating layer 12 for its next contact with the photoconductive layer 10 of the drum 6.

I have developed a number of modifications both of the electrophotographic device described hereinbefore and of the procedure for developing the electrostatic image into a visual image. The various modifications of the electrophotographic device are shown in FIGS. 2 through 6. For example, in the modification shown in FIG. 2 the drum 6 is the same as in FIG. 1 but the drum 7' is different in that the central metal core 11 is smaller than that of FIG. 1 and there is positioned about its periphery a resilient rubber layer 20. Any commercial type of rubber of hardness suflicient to establish intimate contact of the outer insulating layer -12 with the surface of the photoconductive layer 10 may be used for this purpose. Coated upon the exterior of the rubber layer 20 is a conductive layer 2 1. This conductive layer need not be transparent nor have any properties other than low electrical resistance. Thus, the conductive layer 21 may be made of an electrodeposited metallic layer, of an evaporated metallic layer, or of a chemically deposited metallic layer. It may be a metal or a conventional semi-conductor of very low electrical resistance. In any event it should be thin enough to bend readily with the surface of the underlying rubber layer and adhere well to the rubber surface. Over this conductive layer 21 is a thin insulating layer 12 made up of one of the high resistance plastics or other materials mentioned previously. The drum 7 thus produced is then placed in the position of the drum 7 shown in FIG. 1, and the operation of this device is identical with that described in connection with FIG. 1. The resilient rubber backing for the conductive metal layer 21 permits the insulating layer 12 to make more uniform contact with the photoconductive layer in spite of minor irregularities in the symmetry of these two adjoining layers.

' The modification of the electrophotographic device shown in FIG. 3 embodies a photoconductive drum 6 which is identical with the corresponding drum in FIG. 1. The second element of the electrophotographic device comprises a drum 7 substantially the same as that shown in FIG. 1. In order to spare the surface of the drum 7 from the slightly abrasive action of the developer powder which is applied to and removed from the drum 7 in the embodiments of FIGS. 1 and 2, a third drum 23 is positioned in rolling contact with the drum 7. The drum 23, like drum 7, is composed of an inner metal component 11 and an outer insulating layer 12. The electrostatic image established on the surface of the insulating layer 12 of the drum 7 is transferred to the corresponding surface of the drum 23 along the line of contact between these two drums. The electrostatic image on the drum 23 is then developed through the medium of the coating zone 22 and the developed image is transferred to the paper 17 at the transfer zone 16, and the surface of the drum is prepared for further use by cleaning and discharging zones 18 and 19, respectively, such as those described in connection with FIG. 1.

In lieu of drum-shaped or cylindrical elements, one or both of these elements may be in the form of a flat bed. For example, as shown in FIG. 4, the photoconductive element corresponding to the drum 6 in FIG. 1 comprises a glass plate or other transparent backing material 8', a transparent conductive layer 9, and a high resistance photoconductive layer 10. These layers are similar to those more fully described in conjunction with FIG. 1. Placed immediately below this plate-like element is a positive 14 of the image to be reproduced. Below this and positioned so as to illuminate the photoconductive layer through this positive image is placed a light source 13'. Positioned so as to roll across the surface of this photoconductor is a drum-shaped element constructed the same as drum 7 in FIG. 2. Electrical contact is estbalished between the transparent conductive coating 9' on the plate element and the metal roller core 11 (and hence the flexible metal layer 21), and a battery 15 is inserted between these two conducting layers. As the roller progresses across the flat plate a charged image is developed on the surface of the insulating layer 12 of the roller. This image then moves with the revolving drum through a developing area 22 and the visual image is removed on the paper 17. Positioned peripherally of the drum element immediately after the removal of the image are cleaning and discharging zones 18 and 19. Upon completion of one traverse of the photoconductive plate element, the drum element stops, is lifted off and is returned to its starting position by any conventional mechanism.

The modification shown in FIG. 5 is one in which both of the elements are in the form of a flat plate. In this modification the entire electrostatic charge image is developed at one time as distinguished from the line-at-atime development of the electrostatic image on the insulating surface of the drum 7 in the modifications shown in FIGS. 1 through 4. The plate-shaped photoconductive element of the device shown in FIG. 5 is the same as that shown in FIG. 4. The second flat element of the device of FIG. 5 comprises a rigid metal backing plate 24, a resilient layer 25 of rubber or similar composition, a conducting layer 21, and an insulating layer 12'. This second plate-shaped element is brought into contact with the photoconductive surface of the first plate element. A positive 14 of the object to be reproduced is placed beneath the bottom surface of the glass layer 8 and illuminated from a light source 13'. Simultaneous with this potential is applied between the metallic conducting layer 21' and the transparent conducting layer 9'. With these conditions maintained, a charge is built up on the surface of the insulating layer 12' and the photoconductive surface 10' in non-illuminated areas. In illuminated areas little or no charge will be developed. These two layers are then separated while both the illumination and the potential are maintained. This produces a charge configuration on the surface of the insulating layer 12 and the surface of the photoconductive layer 10 which is inversely proportional to the transparency of the original image. This is then transported to an adjacent area, and developing means similar to those used to render this image visible in the procedures described herein are employed. The image is then removed by conventional means. This process is adaptable to flatbed printing processes and can be incorporated into a standard printing operation.

As mentioned hereinbefore, I have developed an improvement in the procedure for developing the electrostatic image into a visual image. This procedure of my invention employs the step of applying the developing powder, such as carbon black, in the form of a dispersion in an electrically insulating liquid. Although any of the other conventional finely divided solid materials used heretofore for the visual development of an electrostatic image may be the solid component of this liquid dispersion, carbon black is presently preferred. Accordingly, although care bon black will be referred to exclusively hereinafter and in the claims, it must be understood that the other conyentional electrically non-conductive powders may be substituted for the carbon black.

Liquids which I have found suitable for this purpose include such organic liquids as carbon tetrachloride, various hydrocarbons and conventional insulating oils. I have also found that inorganic liquids, such as high purity Water, may also be used satisfactorily in practicing the invention. The carbon powder, after suitable drying and cleaning, is added to the liquid and is milled in a ball mill for an extended period of time sufiicient to reduce the carbon particle size to the desired maximum of 1 micron or less. I have found that when an electrostatic image is immersed in a dispersion of this type, the carbon is deposited on the charged areas in a faithful reproduction of the original electrostatic image. This deposition of carbon has been found to be enhanced by placing a metal electrode spaced closely to the surface of the electrostatic image and flowing the liquid developer between these two surfaces. The precipitation of the carbon particles is thus accelerated and there results a very uniform continuous-tone image. This procedure is adaptable, in addition to the aforementioned printing process, to all forms of electrophotography, and in particular I have found this liquid development procedure to be highly satisfactory for line drawing applications as for continuous-tone work.

As alternative modification of the foregoing procedure which I have found to be highly adaptable to the aforementioned printing operation and also to other forms of electrostatic photography and image production is using a cylidrical applicator as through the coating of an insulating roller with the fine carbon liquid suspension and then moving the thus-coated roller over the electrostatic image on the surface of the insulating layer. The developer powder is thus transferred from the surface of the roller to the charged areas of the electrostatic image whereas in uncharged areas of the image the carbon is permitted to remain attached to the roller. A flexible roller, advantageously of rubber, is preferred for this purpose as it conforms more faithfully to the surface irregularities of the print. The roller must of course be covered uniformly with the developer powder layer. To accomplish this, the roller is coated with or immersed in this liquid developer comprising the aforementioned suspension of carbon black in an insulating organic liquid vehicle and is drained so as to leave a thin layer of the developer completely and uniformly distributed over the surface of the rubber roller. This layer is held on by surface tension and the roller may be left wet with the developer liquid or may be allowed to dry before it is rolled over the surface of the electrostatic image. I have found both procedures to work equally well.

Present developing methods for electrostatic images include dry powder spraying, dusting and rolling with beads of the opaque developer solid. The dry powder method requires bulky equipment and many auxiliary devices for both charging the powder cloud and for applying the powder cloud to the electrostatic image to be developed. The main disadvantage of this method is the minimum size particle which can be readily suspended in air. This, of course, limits the resolution obtainable in the final image. Further disadvantages of the powder cloud technique is the relatively slow rate at which it can be accomplished and its lack of adaptability to a continuous process. The liquid development method of my invention eliminates both of these latter disadvantages, and the maximum particle size which can be adapted to my procedure is that of colloidal particles and for this reason all particles in the liquid suspension are well below the maximum resolution of a silver halide print. Furthermore,- no electrostatic charging of the developer powder-liquid vehicel suspension is required in the practice of my invention, and this is an advantage over the prior art powder cloud techniques which require powdercharging apparatus.

An inherent disadvantage in both the liquid suspension technique of my invention and the dry powder cloud technique of the prior art is the halo effect which is exhibited to a noticeable extent. Halo may be described as a dark ring around a light area or a white ring around a dark area. The chief cause of this phenomenon is the field existing between adjacent charged and uncharged areas. The deposition of the developer powder in both the dry powder cloud procedure and the liquid suspension procedure is essentially a field phenomenon, with the cloud or the liquid respectively being utilized principally to bring the carbon particles close to the surface to be developed. At this surface, the electric fields existing due to the charge configuration on the insulating material act upon the particles and cause them to be deposited in various areas. A halo results because of the fundamental electrical parameters of these differing field areas. This halo formation is minified by the use of a development electrode spaced close to the surface under development and tied electrically to the backing layer. This expedient, however, does not eliminate the halo effect. On the other hand, the roller development technique of my invention completely eliminates the halo formation inasmuch as the roller brings the carbon particles directly and forcefully into contact with the surface to be developed and the electrostatic charge holds these particles at their deposited positions on the surface of the plate under development. No field is required to transfer the particles to the surface of the plate, and consequently the halo effect is eliminated.

An outstanding advantage of this roller ty-pe development technique of my invention is its adaptability to a high speed repetitive printing process. By employing as the developing stage a roller rotating in the aforementioned liquid developer bath, a process similar to commercial printing processes results in which the aforementioned electrophotographic device of my invention is embodied.

The developing roller need not necessarily coact with the element containing the insulating material, although the structure and operation of the apparatus of my invention has been so described hereinbefore in the in terest of simplicity. Inasmuch as the charge configuration corresponding to the illumination image is built up upon both the insulating layer 12 and the photoconductive layer 10, it will be readily appreciated that what has been'said hereinbefore with respect to the development of a visual image from the electrostatic image on the insulating layer applies also to the development of a visual image from the corresponding electrostatic image on the photoconductive layer. This arrangement is illustrated in FIG. 6 wherein the developer tray 22 is disposed beneath the drum 6 so as to develop the image on the photoconductive layer 10 rather than being disposed beneath the drum 7 as in FIG. 1. Thus, the visual image may be formed on either or both of these layers with consequent flexibility of operation not heretofore enjoyed.

I claim:

1. The process of developing a high resolution reproduction comprising:

(a) forming on the surface of a photoconductive insulating layer in an exposure zone a latent electrostatic charge pat-tern conforming in configuration to an original to be reproduced by means of optical exposure of said photoconductive insulating layer to said original while the portion of the layer being exposed is subjected to a potential difference sufficient to produce an electrostatic charge pattern thereon and (b) moving the photoconductive insulating layer from the exposure zone into and continuously through a development zone spaced from the exposure zone, and applying in the development zone colloidal sized marking particles to the charge pattern on said photoconductive insulating layer from a liquid developer comprising a colloidal dispersion of said marking particles in an electrically insulating continuous phase liquid vehicle, and

(c) maintaining said liquid developer in contact with said photoconductive insulating layer in the development zone until suflicient marking particles deposit and reproduce said latent electrostatic charge pattern in visible particle configuration.

2. The process of claim 1 including applying said liquid developer and developing said latent electrostatic charge pattern while said photoconductive insulating layer is positioned closely adjacent to an electrical conductor and while dielectric conditions are maintained between said photoconductive insulating layer and said electrical conductor causing deposition of said colloidal marking particles as controlled by the electrostatic field between said latent electrostatic charge pattern and said conductor.

3. A xerographic reproduction process comprising:

(a) moving a member having a layer of photoconductive insulating material on one surface into an exposure zone,

(b) forming on the surface of the photoconductive insulating layer in the exposure zone a latent electrostatic charge pattern conforming in configuration to original to be reproduced by means of optical exposure of the photoconductive insulating layer to the original while the portion of the layer being exposed is subjected to a potential difference sufficient to produce an electrostatic charge pattern thereon,

(c) moving the member having the layer of photoconductive insulating material and the charge pattern thereon from the exposure zone into and continuously through a development zone spaced from the exposure zone,

(d) applying to the photoconductive insulating layer during its passage through the development zone a liquid developer comprising a dispersion of manking particles in an electrically insulating continuous phase liquid vehicle, and

(e) maintaining said liquid developer in contact with said photoconductive insulating layer in the development zone until sufficient marking particles deposit and reproduce said latent electrostatic charge pattern in visible particle configuration.

4. The method of producing a visual reproduction of a visible object which comprises:

directing a light image of said object in an exposure zone first onto a photoconductive element comprising a transparent layer of electrically conductive material through which said light image passes to a contiguous high resistance photoconductive layer secured to and supported by said electrically conductive material while said layer is contiguous to an adjacent contacting but separable electrostatic image-forming element comprising a layer of electrically insulating material backed by and in contact with a supporting conductive layer having low electrical resistance;

applying to the supporting layer an electric potential with respect to the transparent layer of electrically conductive material and thus establishing an electrostatic reproduction of said light image on the surface of said layer of insulating material contiguous to the intermediate layer of photoconductive material;

separating the electrostatic image-bearing element from the photoconductive element;

and thereafter moving the surface of the insulating material which has been contiguous to the surface of the high resistance photoconductive material from the exposure zone continuously into and through a development zone spaced from the exposure zone, and applying to the surface of the insulating material in the development zone a liquid developer comprising a dispersion of marking particles in an electrically insulating liquid vehicle in a continuous phase With the resulting formation of a deposit of marking particles on the said surface of the insulating material comprising a visual reproduction of said light image, said marking particles comprising finely divided solid materials.

5. The method of claim 4 in which said electrically insulating liquid vehicle comprises an organic material.

6-. The method of claim 4 in which the marking particles comprising the visual reproduction of said light image formed on said surface of the insulating material are transferred to a transfer Web.

7. In the method of producing a visual reproduction of a visual object wherein an electrostatic image of the object is formed on a surface of an electrically insulating material and the resulting electrostatic image is developed into a visible image, the improvement which comprises: forming a latent electrostatic image of the object on a surface of an electrically insulating material; applying a liquid developer to the surface of an electrically non-conductive cylindrical applicator in the form of a dispersion of solid particles in an electrically insulating organic liquid vehicle, and thereafter transferring this dispersion to the elecstatic image-bearing surface of said insulating material by rolling said applicator in contact with said surface of said insulating material with the resulting formation of a visual image composed of said solid particles in a pattern conforming to the aforesaid electrostatic image. *8. In the method of producing a visual reproduction of a visual object wherein an electrostatic image of the object is formed on a surface of an electrically insulating material and the resulting electrostatic image is developed 10 into a visible image, the improvement which comprises: forming a latent electrostatic image of the object on a a surface of an electrically insulating material; applying a liquid developer to the surface of an electrically non-conductive cylindrical applicator in the form of a dispersion of solid particles in an electrically insulating organic liquid vehicle,

drying the applied dispersion on the surface of the applicator,

and thereafter transferring the resulting deposit of solid particles from the applicator to the electrostatic image-bearing surface of said insulating material by rolling said applicator in contact with said surface of said insulating material with the resulting formation of a visual image composed of said solid particles in a pattern conforming to the aforesaid electrostatic image.

9. A process for developing an electrostatic charge pattern on an insulating surface in making an electrophotographic reproduction comprising applying with a cylindrically shaped electrically nonconductive member a continuous liquid developer composition comprising a dispersion of finely divided solid marking particles in an electrically insulating continuous phase liquid to said surface whereby said marking particles are electrostatically attracted to said surface and deposit thereon in conformity with the electrostatic charge pattern.

10. The process according to claim 9 in which said insulating surface comprises a surface of a photoconductive insulating layer of an electrophotographic plate.

11. In a method of forming developed xerographic images in which a photoconductive insulating layer is positioned in an exposure zone facing and in physical contact with an electrode including a high electrically resistant surface layer in facing contact with said photoconductive layer and in which simultaneously with exposure of said photoconductive insulating layer there is applied an intense electric field to cause charge deposition of a developable charge pattern on said adjacent facing layer of said high resistant layer in accordance with an image pattern and a developable charge pattern on said photoconductive layer in accordance with said image pattern to which said photoconductive insulating layer is exposed,

the improvement comprising moving the photoconductive insulating layer from the exposure zone into and continuously through a development zone spaced from the exposure zone, and

applying to the surface of the photoconductive insulating layer in the development zone a liquid developer comprising solid particles in an electrically insulating continuous phase liquid so as to develop said electrostatic charge pattern conforming in configuration to said image pattern on the surface of said photoconductive insulating layer with solid particles from the liquid developer.

12. A xerographic reproduction process for developing an electrostatic charge pattern produced in an exposure zone on an insulating surface of an electrophotographic light sensitive member capable of producing a pattern of charge in correspondence to a light and shadow pattern to which it is exposed, which comprises moving the surface bearing the electrostatic charge pattern from the exposure zone into and continuously through a development zone and applying to the surface in the development zone a continuous liquid developer composition comprising a dispersion of finely divided marking particles in an electrically insulating continuous phase liquid to said surface whereby said marking particles are electrostatically attracted to said surface and deposit thereon in conformity with the electrostatic charge pattern,

and transferring the deposited marking particles from said surface to a new support base.

13. A process for developing an electrostatic charge pattern produced in an exposure zone on an insulating surface in making an electrophotographic print, which comprises moving the surface bearing the electrostatic charge pattern from the exposure zone into and continuously through a development zone and immersing said surface in the development zone in a 5 References Cited UNITED STATES PATENTS Neville 118-259 Kaufmann 117-160 X Scott 95-1.7 Pirie et al. 117-39 Wynd 117-17.5 Carlson 95-1.7 Carlson 95-1.7 Carlson 95-1.7 George et al 117-37 Adams 117-111 Fox 117-17.5 De Forest et al 117-37 1 2 5/ 1951 Carlson 95-1.7 7/ 1951 Hooper 95-1.7 11/1951 Walkup et al 117-17.5 11/1951 Hooper 95-1.7 4/ 1953 Pethick 95-1.7 8/1953 Ebert 117-17.5 X 10/ 1953 Weimer 315-10 2/1954 Pearson 11717.5

11/1954 Butterfield 117-17.5 X 7/1956 Jacob 117-17.5 3/1957 Walkup 117-17.5 10/1957 Greig 11717.5 2/1958 Fauser et al 118-637 3/1958 Walkup 118-637 3/ 1958 Atkinson et al 117-37 5/1958 Walkup 117-17.5

FOREIGN PATENTS 10/19221 Great Britain 117-17.S 4/1937 Great Britain 951.7

WILLIAM D. MARTIN, Primary Examiner 25 M. SOFOCLEOUS, Assistant Examiner US. Cl. X.R.

117-37 LE; 118-637, DIG. 23; 355-10 

